What makes CD-ROM attractive or unattractive in the library setting? What are its advantages or disadvantages? How will the technology develop? What has been the experience of libraries who have tested and introduced CD-ROM products to their users? The following two-part article addresses these questions. Part 1 explores the development of disk technology, its advantages and disadvantages and potential library applications. The actual testing and use of one of the CD-ROM products, PsycLIT, is the focus of Part II.